For copper alloys for electronic materials used in various electronic parts such as connectors, switches, relays, pins, terminals, lead frames etc., it is desired to satisfy both high strength and high electrical conductivity (or thermal conductivity) as basic properties. In recent years, high integration as well as reduction in size and thickness of electronic parts have rapidly advanced, and in correspondence, the desired level for copper alloys used in electronic device parts are becoming increasingly sophisticated.
In regards to high strength and high electrical conductivity, the amount of precipitation hardened copper alloy used as the copper alloy for electronic materials, in place of solid solution strengthened copper alloys such as conventional phosphor bronze and brass, have been increasing. In precipitation hardened copper alloys, fine precipitates uniformly disperse by age-treating a solutionized supersaturated solid solution to increase alloy strength, and at the same time the amount of solutionized element in copper decrease to improve electrical conductivity. As a result, a material having mechanical characteristics such as strength and spring property as well as good electrical and thermal conductivity can be obtained.
Among precipitation hardened copper alloys, a Cu—Ni—Si copper alloy generally referred to as the Corson alloy is a representative copper alloy that possesses the combination of relatively high electrical conductivity, strength, and bendability, making it one of the alloys that are currently under active development in the industry. In this copper alloy, improvement of strength and electrical conductivity is attempted by allowing microfine Ni—Si intermetallic compound particles to precipitate in the matrix phase.
Recently, attention is paid to Cu—Ni—Si—Co system alloys produced by adding Co to Cu—Ni—Si system copper alloys, and technology improvement is in progress. Japanese Patent Application Laid-Open No. 2009-242890 (Patent Document 1) describes an invention in which the number density of second phase particles having a particle size of 0.1 μm to 1 μm is controlled to 5×105 to 1×107/mm2, in order to increase the strength, electrical conductivity and spring bending elastic limit of Cu—Ni—Si—Co system alloys.
This document discloses a method for producing a copper alloy, the method including conducting the following steps in order: step 1 of melting and casting an ingot having a desired composition; step 2 of heating the material for one hour or longer at a temperature of from 950° C. to 1050° C., subsequently performing hot rolling, adjusting the temperature at the time of completion of hot rolling to 850° C. or higher, and cooling the material with an average cooling rate from 850° C. to 400° C. at 15° C./s or greater; step 3 of performing cold rolling; step 4 of conducting a solution treatment at a temperature of from 850° C. to 1050° C., cooling the material at an average cooling rate of greater than or equal to 1° C./s and less than 15° C./s until the material temperature falls to 650° C., and cooling the material at an average cooling rate of 15° C./s or greater until the material temperature falls from 650° C. to 400° C.; step 5 of conducting a first aging treatment at a temperature of higher than or equal to 425° C. and lower than 475° C. for 1 to 24 hours; step 6 of performing cold rolling; and step 5 of conducting a second aging treatment at a temperature of higher than or equal to 100° C. and lower than 350° C. for 1 to 48 hours.
Japanese Patent Application National Publication Laid-Open No. 2005-532477 (Patent Document 2) describes that in a production process for a Cu—Ni—Si—Co alloy, various annealing can be carried out as stepwise annealing processes, so that typically, in stepwise annealing, a first process is conducted at a temperature higher than that of a second process, and stepwise annealing may result in a more satisfactory combination of strength and conductivity as compared with annealing at a constant temperature.
JP 2006-283059 A (Patent Document 3) describes a method for manufacturing high strength copper alloy plate for the purpose of producing Corson (Cu—Ni—Si) copper alloy plate having electrical conductivity of 35% IACS or greater, yield strength of 700 N/mm2 or greater and excellent bendability. The method comprises steps of performing hot rolling to an ingot of copper alloy and quenching as necessary; and then performing cold rolling; annealing continuously so as to obtain recrystallized structure and solid solution; and then conducting cold rolling at a reduction ratio of up to 20% and aging treatment at 400-600° C. for 1 hour to 8 hours; and then final cold rolling at a reduction ratio of 1-20%; and then performing annealing at 400-550° C. for up to 30 seconds.